1. Technical Field
The present disclosure generally relates to the field of electronics. More particularly, the present disclosure relates to radio frequency (RF) switches with low oxide stress.
2. Related Art
High frequency switches are used in wireless communications and radar systems for switching between the transmit (Tx) and receive (Rx) paths, for routing signals to the different blocks in multi-band/standard phones, for RF signal routing in phase shifters used in phased array antennas, etc. The communication frequencies cover a broad range from the below-a-megahertz AM band, to the commercial FM band (88-108 MHz), to various military hand-held radio transceivers up to approximately 400 MHz, and to the cellular frequencies of around 900 MHz and 2.4 GHz. State-of-the-art switch technology uses solid-state semiconductor devices for their integration compatibility and relatively lower manufacturing cost attributed to batch fabrication. With the conventional approach, the wide spectrum of communication frequencies calls for different switch technologies for different frequency applications.
Wireless communication devices may be composed of a transmit chain and a receive chain, with the antenna and the transceiver circuit being a part of both the transmit chain and receive chain. The transmit chain may additionally include a power amplifier for increasing the output power of the generated RF signal from the transceiver, while the receive chain may include a low-noise amplifier for boosting the weak received signal so that information can be accurately and reliably extracted therefrom.
The low-noise amplifier and the power amplifier may together consist of a front-end module or front-end circuit, which also includes an RF switch circuit that selectively interconnects the power amplifier and the low-noise amplifier to the antenna. The connection to the antenna is switchable between the receive chain circuitry (i.e., the low-noise amplifier and the receiver) and the transmit chain circuitry (i.e., the power amplifier and the transmitter). In time domain duplex (TTD) communications systems where a single antenna is used for both transmission and reception, switching between the receive chain and the transmit chain occurs rapidly many times throughout a typical communications session.
The RF switches and the amplifier circuits of the front-end module are typically manufactured as an integrated circuit. In high-power applications such as GSM (Global System for Mobile communications) handsets, WLAN (wireless local area networking) client interface devices and infrastructure devices, the ICs are typically manufactured with a GaAs (gallium arsenide) semiconductor substrate. The SOI (silicon-on-insulator) process has also found use in RF switch circuit applications. Good insertion loss and isolation are possible with both GaAs and SOI processes, but manufacturing costs tend to be higher in comparison to more conventional semiconductor technologies, such as the CMOS (Complementary Metal Oxide Semiconductor) process. There have been attempts to implement RF switches in the CMOS process, but only low power devices have been realized. This is, in part, due to the parasitic capacitance of transistors and low-resistivity substrates of bulk semiconductor wafers used in the CMOS process. Accordingly, high-isolation high-linearity CMOS switches at large RF signal levels have been difficult to achieve.
Several electrical parameters are associated with the performance of RF switch designs, but four are considered to be of fundamental importance to the designer because of their strong interdependence: insertion loss, isolation, switching time and power handling. Insertion loss refers to power loss in the RF switch, and is expressed in dB. It is defined by Pout-Pin (dB), where Pin is the input power applied to the RF switch, and Pout is the power at the output port of the RF switch. Thus, a goal of RF switches is to minimize insertion loss. Isolation is a measure of how effectively a switch is turned off. It refers to the measure of the signal attenuation between the active signal port and the inactive signal port. The main contributing factors include capacitive coupling and surface leakage. Thus, a goal of RF switches is to maximize isolation, which minimizes signal leakage. Return loss generally refers to the amount by which the undesired return (or reflected) transmit signal is attenuated. It refers to the measure of input and/or output matching conditions, and is expressed in dB. Linearity, or power handling capability, is the capability of the RF switch to minimize distortion at high power output levels and is expressed in dBm. It is typically represented by the 1 dB compression point (P1 dB), or the point at which insertion loss is degraded by 1 dB. Thus, a goal of RF switches is to maximize linearity. Switching time is the period of time a switch needs for changing state from “ON” to “OFF” and “OFF” to “ON.” This period can range from several microseconds in high-power switches to a few nanoseconds in low-power, high-speed devices.
RF switches are designed to generate as little harmonic distortion as possible. Governmental standards also restrict the output of spurious emissions including those from harmonic distortion to either −70 dBc or 43+10 log(P). Conventional front end circuits, including the RF switch, may be fabricated on a bulk CMOS (complementary metal oxide semiconductor) substrate. However, there is a performance tradeoff between insertion loss and harmonic distortion under large signal operation. Furthermore, because of low mobility, low breakdown voltage, and high substrate conductivity associated with CMOS devices, an RF switch with low insertion loss, high isolation, wide bandwidth, and linearity is difficult to produce.
The main performance characteristics of an RF switch are the insertion loss in the ON-state, the isolation in the OFF-state, the return loss in both states, the power consumption, bandwidth, power handling capability and the linearity. RF switching is presently realized for the greater part with PIN diode and GaAs MESFET, HEMT, JFET or silicon SOI based semiconductor switches. RF switches are used in a variety of applications, such as traditional single pole multi throw switches (e.g., for general purpose switching, band/mode switching and antenna diversity applications), double pole double throw (DPDT) switches and antenna switch modules (ASM). Highly linear band or mode switches are vital for multi-mode and multi-band architectures as mobile phone radios can easily operate in 14 bands or more. Typically single-pole, double-throw (SPDT) or single-pole, three-throw (SP3T) switches are used depending on the number of bands supported.
There is a continuing need in the art for improved RF switches, whether single pole-double throw, single pole-triple throw, dual port-dual throw, or any other switch type. There is a need to provide a circuit arrangement with a RF switch circuit having faster switching time. There is a need for RF switches that can be implemented on CMOS substrates or any other semiconductor technology while minimizing insertion loss and maximizing isolation and linearity. There is a need for silicon RF switches with high power handling capabilities.